Source-dependent address resolution

ABSTRACT

Systems and method are provided for source-dependent address resolution. Multiple computing devices may be associated with identifiers, such as network names. These computing devices may further be associated with both internally and externally accessible network addresses. A source-dependent address resolution component may resolve a network identifier into an internal or external address based on a network of a requesting device. Specifically, a request for address resolution may be received from a source network, and be resolvable into an address of a target network. If the source network and target network are the same, an internal address of that shared network is returned. If the source network and the target network are different, an external address enabling external communication with the target network is returned. In some embodiments, determination of a source network may be facilitated based on a source port of a request.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/739,627, entitled SOURCE-DEPENDENT ADDRESSRESOLUTION, and filed on Dec. 19, 2012, the entirety of which is herebyincorporated by reference.

BACKGROUND

Generally described, computing devices utilize a communication network,or a series of communication networks, to exchange data. Companies andorganizations operate computer networks that interconnect a number ofcomputing devices to support operations or provide services to thirdparties. The computing systems can be located in a single geographiclocation or located in multiple, distinct geographic locations (e.g.,interconnected via private or public communication networks).Specifically, data centers or data processing centers, herein generallyreferred to as a “data center,” may include a number of interconnectedcomputing systems to provide computing resources to users of the datacenter. The data centers may be private data centers operated on behalfof an organization or public data centers operated on behalf, or for thebenefit of, the general public.

To facilitate increased utilization of data center resources,virtualization technologies may allow a single physical computing deviceto host one or more instances of virtual machines that appear andoperate as independent computing devices to users of a data center. Withvirtualization, the single physical computing device can create,maintain, delete or otherwise manage virtual machines in a dynamicmatter. In turn, users can request computer resources from a datacenter, including single computing devices or a configuration ofnetworked computing devices, and be provided with varying numbers ofvirtual machine resources.

Generally, the physical networks include a number of hardware devicesthat receive packets from a source network component and forward thepacket to a recipient network component. The packet routing hardwaredevices are typically referred to as routers. With the advent ofvirtualization technologies, networks and routing for those networks cannow be simulated using commodity hardware rather than actual routers. Asthe scale and scope of data centers has increased, provisioning andmanaging the physical and virtual computing resources of a data centerhas become increasingly complicated.

Specifically, in one aspect, a third party data center provider may hosta number of virtual machine instances that function as a hosted virtualmachine network for users of the data center. Within a hosted virtualmachine network, each virtual machine instance may be addressable toother virtual machine instances based on an internal addressing scheme.In addition, one or more virtual machine instances may also beaddressable by other computing devices (e.g., physical computing devicesor other virtual machine instances) from outside the hosted virtualmachine network based on an external addressing scheme. Still further,each virtual machine instance may be associated with a host name,enabling human-readable (or substantially human-readable) identificationof the virtual machine instance. In traditional systems, host names maybe resolvable to network addresses based on a Domain Name System (DNS).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisdisclosure will become more readily appreciated as the same becomebetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating an embodiment of a substratenetwork having computing nodes associated with a virtual computernetwork;

FIG. 2 is a block diagram of the substrate network of FIG. 1illustrating logical networking functionality;

FIG. 3 is a block diagram of the substrate network of FIG. 1illustrating a substrate network configuration associated with overlaynetworks;

FIGS. 4A and 4B are block diagrams of the substrate network of FIG. 1illustrating independently determined substrate routing;

FIGS. 5A and 5B are block diagrams of the substrate network of FIG. 1illustrating virtual route selection propagation to the substratenetwork;

FIG. 6 is a block diagram of the substrate network of FIG. 1illustrating the determination of routes into or out of a virtualnetwork by network translation device;

FIG. 7A illustrates a flow diagram for a process of propagating virtualroutes to a substrate network;

FIG. 7B illustrates a flow-diagram for a process of determiningsubstrate routing based on target performance characteristics of theassociated virtual network;

FIG. 8 is a simplified block diagram of the substrate network of FIG. 1illustrating hosted virtual machine networks;

FIG. 9 is a simplified block diagram of the substrate network of FIG. 1illustrating the allocation of network resources to a virtual computingdevice of a hosted virtual machine network;

FIGS. 10A and 10B are block diagrams of the simplified substrate networkof FIG. 1 illustrating resolution of a virtual computing device addressbased on a source network of an address resolution request; and

FIG. 11 is an illustrative routine for determining a virtual computingdevice address based on a source network of an address resolutionrequest.

DETAILED DESCRIPTION

Generally described, aspects of the present disclosure relate to themanagement of virtual machine instances. Specifically, embodiments ofpresent disclosure relate to the resolution of network addresses basedon virtual computing device identifiers (e.g., virtual machine names).One or more virtual computing devices may be associated with both aninternal network address and an external network address. Internalnetwork addresses may be utilized to route communications betweenhosted, virtual computing devices that art part of a hosted virtualmachine network. External network address may enable communicationbetween virtual computing devices of disparate hosted virtual machinenetworks, or between a virtual computing device and any other deviceexternal to a specific virtual machine network.

In order to provide flexibility to internal or external addressing, aswell as to facilitate human identification of virtual computing devices,each virtual computing device may be associated with an identifier. Aswill be discussed in more detail below, a source-dependent addressresolution component may enable intelligent resolution of virtualcomputing device identifiers to network addresses. Specifically, wherean address resolution request is received from a source virtualcomputing device that is associated with a common hosted virtual machinenetwork to a targeted virtual computing device, an internal addressrepresentative of the target virtual computing device may be provided.One skilled in the relevant art will appreciate that the internaladdress can correspond to any range of network addresses selected forthe hosted virtual network regardless of any physical network addressesassociated with the underlying physical computing devices utilized tohost the virtual instances. However, where an address resolution requestis received from a device not associated with the hosted virtual machinenetwork of a targeted virtual computing device, an external address ofthe target virtual computing device may be provided. The externaladdress is generally addressable by other virtual components or physicalcomputing devices via a communication network. Such source-dependentaddress resolution may enable efficient use of network resources byminimizing routing within hosted virtual machine networks. In addition,such source-dependent address resolution may ensure the privacy ofinternal addresses.

Illustratively, a network can have one or more devices configured toreceive DNS queries from computing devices, generally referred to as DNSservers. A DNS server can process the DNS query and return one or morenetwork addresses responsive to a particular DNS query. In anembodiment, one or more DNS servers can include a source-dependentaddress resolution component that may be configured to identify a sourcenetwork of a request based on information within the request, such as asource address. Illustratively, the source network identifier may be acommon identifier used by components of a given hosted virtual network.In other embodiments, the source network identifier may be configured ina manner to identify individual components of a hosted virtual networkor groups of components of a hosted virtual network.

In some embodiments, a source address alone may be insufficient toidentify a source network of a request. For example, where multiplevirtual computing devices of multiple hosted virtual machine networksare hosted within a single physical computing device, address resolutionrequests from any of the virtual computing devices may appear to comefrom the same source address: that of the host physical computingdevice. Accordingly, it may be unclear from which of the multiple hostedvirtual machine networks the request was transmitted. In someembodiments, data encapsulation techniques (such as those discussed inmore detail below) may be utilized in order to correctly identify asource address of an address resolution request. For example, wheremultiple virtual computing devices are hosted within a single physicalcomputing device, requests from any virtual computing device may beencapsulated at the physical computing device before being forwarded(e.g., to the source-dependent address resolution component). Prior todecapsulation, these packets would appear to contain a source address ofthe physical computing device. However, after decapsulation, the packetswould contain a source address of the virtual computing device,therefore enabling correct source-dependent address resolution.

In some embodiments, however, encapsulation and decapsulation of allsource-dependent address resolution requests may be undesirable. Forexample, such encapsulation and decapsulation may require a high amountof processing power, or introduce undesired latency into networkcommunications. Accordingly, in some embodiments, source-dependentaddress resolution may be facilitated, in part, based on a source portof an address resolution request. For example, as noted above, wheremultiple virtual computing devices are hosted within a single physicalcomputing device, address resolution requests from any of the virtualcomputing devices may appear to come from the address of the physicalcomputing device. However, by assigning distinct ports for transmissionof address resolution requests to each virtual computing device,requests from each virtual computing device may be distinguished. Forexample, virtual computing devices ‘A’ and ‘B’ may both be hosted byphysical computing device ‘Z.’ Address resolution requests generated byeither virtual computing device may appear to originate from thephysical computing device ‘Z.’ To resolve such an issue, source port ‘1’may be assigned to virtual computing device ‘A,’ while source port ‘2’may be assigned to virtual computing device ‘B.’ Thereafter, any addressresolution requests from physical computing device ‘Z’ generated atsource port ‘1’ may be attributed to virtual computing device ‘A.’Similarly, any address resolution requests from physical computingdevice ‘Z’ generated at source port ‘2’ may be attributed to virtualcomputing device ‘B.’ By utilization of source-port differentiation,source-dependent address resolution may be implemented by a number ofvirtual computing devices on a single physical computing device, withoutrequiring data packet encapsulation.

The following section discusses various embodiments of managed networksfor network data transmission analysis. Following that is furtherdiscussion of systems and methods enabling source-dependent addressresolution.

Managed Computer Networks for Network Data Transmission Analysis

With the advent of virtualization technologies, networks and routing forthose networks can now be simulated using commodity hardware components.For example, virtualization technologies can be adapted to allow asingle physical computing machine to be shared among multiple virtualnetworks by hosting one or more virtual machines on the single physicalcomputing machine. Each such virtual machine can be a softwaresimulation acting as a distinct logical computing system that providesusers with the illusion that they are the sole operators andadministrators of a given hardware computing resource. In addition, asrouting can be accomplished through software, additional routingflexibility can be provided to the virtual network in comparison withtraditional routing. As a result, in some implementations, supplementalinformation other than packet information can be used to determinenetwork routing.

Aspects of the present disclosure will be described with regard toillustrative logical networking functionality for managed computernetworks, such as for virtual computer networks that are provided onbehalf of users or other entities. In at least some embodiments, thetechniques enable a user to configure or specify a network topology,rousing costs, routing paths and/or other information for a virtual oroverlay computer network including logical networking devices that areeach associated with a specified group of multiple physical computingnodes. For example, a user (e.g., a network administrator for anorganization) or service provider may configure a virtual or overlaynetwork based on detected events, processing criteria, or upon request.With the network configuration specified for a virtual computer network,the functionally and operation of the virtual network can be simulatedon physical computing nodes operating virtualization technologies. Insome embodiments, multiple users or entities (e.g. businesses or otherorganizations) can access the system as tenants of the system, eachhaving their own virtual network in the system. In one embodiment, auser's access and/or network traffic is transparent to other users. Forexample, even though physical components of a network may be shared, auser of a virtual network may not see another user's network traffic onanother virtual network if monitoring traffic on the virtual network.

By way of overview, FIGS. 1 and 2 discuss embodiments wherecommunications between multiple computing nodes of the virtual computernetwork emulate functionality that would be provided by logicalnetworking devices if they were physically present. In some embodiments,some or all of the emulation are performed by an overlay network managersystem. FIGS. 2-4B and 7B discuss embodiments where substrate routingdecisions can be made independently of any simulated routing in theoverlay network, allowing, for example, optimization of traffic on thesubstrate network based on information unavailable to a virtual networkuser. FIGS. 5A-7A discuss embodiments where routing decisionsimplemented on the virtual or overlay network are propagated to thesubstrate network. One skilled in the relevant art will appreciate,however, that the disclosed virtual computer network is illustrative innature and should not be construed as limiting.

Overlay Network Manager

FIG. 1 is a network diagram illustrating an embodiment of an overlaynetwork manager system (ONM) for managing computing nodes associatedwith a virtual computer network. Virtual network communications can beoverlaid on one or more intermediate physical networks in a mannertransparent to the computing nodes. In this example, the ONM systemincludes a system manager module 110 and multiple communication managermodules 109 a, 109 b, 109 c, 109 d, 150 to facilitate the configuringand managing communications on the virtual computer network.

The illustrated example includes an example data center 100 withmultiple physical computing systems operated on behalf of the ONMsystem. The example data center 100 is connected to a global internet135 external to the data center 100. The global internet can provideaccess to one or more computing systems 145 a via private network 140,to one or more other globally accessible data centers 160 that each havemultiple computing systems, and to one or more other computing systems145 b. The global internet 135 can be a publicly accessible network ofnetworks, such as the Internet, and the private network 140 can be anorganization's network that is wholly or partially inaccessible fromcomputing systems external to the private network 140. Computing systems145 b can be home computing systems or mobile computing devices thateach connects directly to the global internet 135 (e.g., via a telephoneline, cable modem, a Digital Subscriber Line (“DSL”), cellular networkor other wireless connection, etc.).

The example data center 100 includes a number of physical computingsystems 105 a-105 d and a Communication Manager module 150 that executeson one or more other computing systems. The example data center furtherincludes a System Manager module 110 that executes on one or morecomputing systems. In this example, each physical computing system 105a-105 d hosts multiple virtual machine computing nodes and includes anassociated virtual machine (“VM”) communication manager module (e.g., aspart of a virtual machine hypervisor monitor for the physical computingsystem). Such VM communications manager modules and VM computing nodesinclude VM Communication Manager module 109 a and virtual machines 107 aon host computing system 105 a, and VM Communication Manager module 109d and virtual machines 107 d on host computing system 105 d.

This illustrative data center 100 further includes multiple physicalnetworking devices, such as switches 115 a-115 b, edge router devices125 a-125 c, and core router devices 130 a-130 c. Switch 115 a is partof a physical sub-network that includes physical computing systems 105a-105 c, and is connected to edge router 125 a. Switch 115 b is part ofa distinct physical sub-network that includes the System Manager module110, and is connected to edge router 125 b. The physical sub-networksestablished by switches 115 a-115 b, in turn, are connected to eachother and other networks (e.g., the global internet 35) via anintermediate communication network 120, which includes the edge routers125 a-125 c and the core routers 130 a-130 c. The edge routers 125 a-125c provide gateways between two or more sub-networks or networks. Forexample, edge router 125 a provides a gateway between the physicalsub-network established by switch 115 a and the interconnection network120, while edge router 125 c provides a gateway between theinterconnection network 120 and global internet 135. The core routers130 a-130 c manage communications within the interconnection network120, such as by routing or otherwise forwarding packets or other datatransmissions as appropriate based on characteristics of such datatransmissions (e.g., header information including source and/ordestination addresses, protocol identifiers, etc.) and/or thecharacteristics of the interconnection network 120 itself (e.g., routesbased on the physical network topology, etc.).

The System Manager module 110 and Communication Manager module 109 canconfigure, authorize, and otherwise manage communications betweenassociated computing nodes, including providing logical networkingfunctionality for one or more virtual computer networks that areprovided using the computing nodes. For example, Communication Managermodule 109 a and 109 c manages associated virtual machine computingnodes 107 a and 107 c and each of the other Communication Managermodules can similarly manage communications for a group of one or moreother associated computing nodes. The Communication Manager modules canconfigure communications between computing nodes so as to overlay avirtual network over one or more intermediate physical networks that areused as a substrate network, such as over the interconnection network120.

Furthermore, a particular virtual network can optionally be extendedbeyond the data center 100, such as to one or more other data centers160 which can be at geographical locations distinct from the first datacenter 100. Such data centers or other geographical locations ofcomputing nodes can be inter-connected in various manners, including viaone or more public networks, via a private connection such as a director VPN connection, or the like. In addition, such data centers can eachinclude one or more other Communication Manager modules that managecommunications for computing systems at that data. In some embodiments,a central Communication Manager module can coordinate and managecommunications among multiple data centers.

Thus, as one illustrative example, one of the virtual machine computingnodes 107 a 1 on computing system 105 a can be part of the same virtuallocal computer network as one of the virtual machine computing nodes 107d 1 on computing system 105 d. The virtual machine 107 a 1 can thendirect an outgoing communication to the destination virtual machinecomputing node 107 d 1, such as by specifying a virtual network addressfor that destination virtual machine computing node. The CommunicationManager module 109 a receives the outgoing communication, and in atleast some embodiments determines whether to authorize the sending ofthe outgoing communication. By filtering unauthorized communications tocomputing nodes, network isolation and security of entities' virtualcomputer networks can be enhanced.

The Communication Manager module 109 a can determine the actual physicalnetwork location corresponding to the destination virtual networkaddress for the communication. For example, the Communication Managermodule 109 a can determine the actual destination network address bydynamically interacting with the System Manager module 110, or can havepreviously determined and stored that information. The CommunicationManager module 109 a then re-headers or otherwise modifies the outgoingcommunication so that it is directed to Communication Manager module 109d using an actual substrate network address.

When Communication Manager module 109 d receives the communication viathe interconnection network 120, it obtains the virtual destinationnetwork address for the communication (e.g., by extracting the virtualdestination network address from the communication), and determines towhich virtual machine computing nodes 107 d the communication isdirected. The Communication Manager module 109 d then re-headers orotherwise modifies the incoming communication so that it is directed tothe destination virtual machine computing node 107 d 1 using anappropriate virtual network address for the virtual computer network,such as by using the sending virtual machine computing node 107 a 1'svirtual network address as the source network address and by using thedestination virtual machine computing node 107 d 1's virtual networkaddress as the destination network address. The Communication Managermodule 109 d then forwards the modified communication to the destinationvirtual machine computing node 107 d 1. In at least some embodiments,before forwarding the incoming communication to the destination virtualmachine, the Communication Manager module 109 d can also performadditional steps related to security.

Further, the Communication Manager modules 109 a and/or 109 c on thehost computing systems 105 a and 105 c can perform additional actionsthat correspond to one or more logical specified router devices lyingbetween computing nodes 107 a 1 and 107 c 1 in the virtual networktopology. For example, the source computing node 107 a 1 can direct apacket to a logical router local to computing node 107 a 1 (e.g., byincluding a virtual hardware address for the logical router in thepacket header), with that first logical router being expected to forwardthe packet to the destination node 107 c 1 via the specified logicalnetwork topology. The source Communication Manager module 109 a receivesor intercepts the packet for the logical first router device and canemulate functionality of some or all of the logical router devices inthe network topology, such as by modifying a TTL (“time to live”) hopvalue for the communication, modifying a virtual destination hardwareaddress, and/or otherwise modify the communication header.Alternatively, some or all the emulation functionality can be performedby the destination Communication Manager module 109 c after it receivesthe packet.

By providing logical networking functionality, the ONM system providesvarious benefits. For example, because the various Communication Managermodules manage the overlay virtual network and can emulate thefunctionality of logical networking devices, in certain embodimentsspecified networking devices do not need to be physically implemented toprovide virtual computer networks, allowing greater flexibility in thedesign of virtual user networks. Additionally, correspondingmodifications to the interconnection network 120 or switches 115 a-115 bare generally not needed to support particular configured networktopologies. Nonetheless, a particular network topology for the virtualcomputer network can be transparently provided to the computing nodesand software programs of a virtual computer network.

Logical/Virtual Networking

FIG. 2 illustrates a more detailed implementation of the ONM system ofFIG. 1 supporting logical networking functionality. The ONM systemincludes more detailed embodiments of the ONM System Manager and ONMCommunication Manager of FIG. 1. In FIG. 2, computing node A is sendinga communication to computing node H, and the actions of the physicallyimplemented modules 210 and 260 and devices of network 250 in actuallysending the communication are shown, as well as emulated actions of thelogical router devices 270 a and 270 b in logically sending thecommunication.

In this example, computing nodes A 205 a and H 255 b are part of asingle virtual computer network for entity Z. However, computing nodescan be configured to be part of two distinct sub-networks of the virtualcomputer network and the logical router devices 270 a and 270 b separatethe computing nodes A and H in the virtual network topology. Forexample, logical router device J 270 a can be a local router device tocomputing node A and logical router device L 270 b can be a local routerdevice to computing node H.

In FIG. 2, computing nodes A 205 a and H 255 b includes hardwareaddresses associated with those computing nodes for the virtual computernetwork, such as virtual hardware addresses that are assigned to thecomputing nodes by the System Manager module 290 and/or theCommunication Manager modules R 210 and S 260. In this example,computing node A has been assigned hardware address “00-05-02-0B-27-44,”and computing node H has been assigned hardware address“00-00-7D-A2-34-11.” In addition, the logical router devices J and Lhave also each been assigned hardware addresses, which in this exampleare “00-01-42-09-88-73” and “00-01-42-CD-11-01,” respectively, as wellas virtual network addresses, which in this example are “10.0.0.1” and“10.1.5.1,” respectively. The System Manager module 290 maintainsprovisioning information 292 that identifies where each computing nodeis actually located and to which entity and/or virtual computer networkthe computing node belongs.

This example, computing node A 205 a first sends an address resolutionprotocol (ARP) message request 222-a for virtual hardware addressinformation, where the message is expected to first pass through alogical device J before being forwarded to computing node H.Accordingly, the ARP message request 222-a includes the virtual networkaddress for logical router J (e.g., “10.0.0.1”) and requests thecorresponding hardware address for logical router J.

Communication Manager module R intercepts the ARP request 222-a, andobtains a hardware address to provide to computing node A as part ofspoofed ARP response message 222-b. The Communication Manager module Rcan determine the hardware address by, for example, looking up varioushardware address information in stored mapping information 212, whichcan cache information about previously received communications.Communication Manager module R can communicate 227 with the SystemManager module 290 to translate the virtual network address for logicalrouter J.

The System Manager module 290 can maintain information 294 related tothe topology and/or components of virtual computer networks and providethat information to Communication Manager modules. The CommunicationManager module R can then store the received information as part ofmapping information 212 for future use. Communication Manager module Rthen provides computing node A with the hardware address correspondingto logical router J as part of response message 222-b. While request222-a and response message 222-b actually physically pass betweencomputing node A and Communication Manager module R, from the standpointof computing node A, its interactions occur with local router device J.

After receiving the response message 222-b, computing node A 205 acreates and initiates the sending of a communication 222-c to computingnode H 255 b. From the standpoint of computing node A, the sentcommunication will be handled as if logical router J 270 a werephysically implemented. For example, logical router J could modify theheader of the communication 265 a and forward the modified communication265 b to logical router L 270 a, which would similarly modify the headerof the communication 265 b and forward the modified communication 265 cto computing node H. However, communication 222-c is actuallyintercepted and handled by Communication Manager module R, whichmodifies the communication as appropriate, and forwards the modifiedcommunication over the interconnection network 250 to computing node Hby communication 232-3. Communication Manager module R and/orCommunication Manager module S may take further actions in this exampleto modify the communication from computing node A to computing node H orvice versa to provide logical networking functionality. For example,Communication Manager module S can provides computing node H with thehardware address corresponding to logical router L as part of responsemessage 247-e by looking up the hardware address in stored mappinginformation 262. In one embodiment, a communication manager or computingnode encapsulates a packet with another header or label where theadditional header specifies the route of the packet. Recipients of thepacket can then read the additional header and direct the packetaccordingly. A communication manager at the end of the route can removethe additional header.

A user or operator can specify various configuration information for avirtual computer network, such as various network topology informationand routing costs associated with the virtual 270 a, 270 b and/orsubstrate network 250. In turn, the ONM System Manager 290 can selectvarious computing nodes for the virtual computer network. In someembodiments, the selection of a computing node can be based at least inpart on a geographical and/or network location of the computing node,such as an absolute location or a relative location to a resource (e.g.,other computing nodes of the same virtual network, storage resources tobe used by the computing node, etc.). In addition, factors used whenselecting a computing node can include: constraints related tocapabilities of a computing node, such as resource-related criteria(e.g., an amount of memory, an amount of processor usage, an amount ofnetwork bandwidth, and/or an amount of disk space), and/or specializedcapabilities available only on a subset of available computing nodes;constraints related to costs, such as based on fees or operating costsassociated with use of particular computing nodes; or the like.

Route Selection on Substrate Network

FIG. 3 illustrates an example embodiment of a substrate network 300having a route manager 336 capable of determining routes for overlaynetworks. The substrate network 300 can be composed of one or moresubstrate components or nodes, such as computing nodes, routing nodes,communication links or the like. In FIG. 3, the substrate network 300includes computing nodes A 302, B 304, C 306, and D 308, which arecapable of simulating various components of one or more associatedoverlay networks. The nodes can be located on the same data center or inmultiple data centers. Computing node A is interconnected to node B vianetwork W 310, node B is connected to node C by network X 312, node C isconnected to node D by network Y 314, and node D is connected to node Aby network Z 316. Networks W, X, Y, and Z can include one or morephysical networking devices, such as routers, switches, or the like, andcan include private or public connections. Components shown in FIG. 3,such as the computing nodes and communication manager modules, canimplement certain of the features of embodiments described above withrespect to FIGS. 1 and 2.

In FIG. 3, nodes A 302, B 304, C 306 and D 308 are associated with arespective Communication Manager module 320, 322, 324 and 326. Thecommunication manager modules can implement certain of the featuresdescribed in the Communication Manager 150, 210, 260 and VMCommunication manager 109 a, 109 b, 109 c, 109 d of FIGS. 1 and 2. Forexample, the Communication Manager module 320 for node A can operate ona hypervisor monitor of the computing node and can direct thecommunication of one or more virtual computing nodes 330, 332, 334 ofnode A. The computing nodes, communication managers and Route Manager336 can be part of the same ONM system. In one embodiment, the computingnodes run the XEN operating system (OS) or similar virtualization OS,with the communication managers operating on domain 0 or the first OSinstance and the virtual computing nodes being domain U or additional OSinstances.

The communication manager modules in FIG. 3 are in communication with aRoute Manager module 336, operating on one or more computing devices,that directs routing for the substrate network 300. In one embodiment,the Route Manager operates as part of the ONM System Manager module 110,290 of FIGS. 1 and 2, with functionally combined into a single module.The Route Manager can be located within a data center or at a regionallevel and direct traffic between data centers. In one embodiment,multiple Route Managers can operate in a distributed manner tocoordinate routing across multiple data centers.

In FIG. 3, two virtual networks are associated with the substratenetwork 300. Virtual network 1 (VN1) has components 338, 340, 342,associated with virtual computing nodes on computing nodes A 302, B 304,and C 306. Virtual network 2 (VN2) has components 344, 346, 348associated with virtual computing nodes on nodes A, C, and D 308.

As the Routing Manager module 336 directs network traffic on thesubstrate network 300, traffic can be directed flexibly and variousnetwork configurations and network costs can be considered. For example,routing paths can be determined based on specified performance levelsfor the virtual networks. In one embodiment, if the user for VN1 isentitled to a higher service level, such as for faster speed (e.g. lowerlatency and/or higher bandwidth), traffic associated with VN1 can berouted on a “fast” path of the substrate network 300. For example, inone embodiment, traffic for “platinum” users is prioritized over trafficfor “gold” and “silver” users, with traffic from “gold” usersprioritized over “silver” users. In one embodiment, at least somepackets of the user with the higher service level are prioritized overpackets of a user with a lower service level, for example, during timesof network congestion. The user may be entitled to a higher levelbecause the user has purchased the higher service level or earned thehigher service level through good behavior, such as by paying bills,complying with the operator's policies and rules, not overusing thenetwork, combinations of the same, or the like.

The Route Manager 336 can store user information or communicate with adata store containing user information in order to determine the targetperformance level for a virtual network. The data store can beimplemented using databases, flat files, or any other type of computerstorage architecture and can include user network configuration, paymentdata, user history, service levels and/or the like. Typically, the RouteManager will have access to node and/or link characteristics for thesubstrate nodes and substrate links collected using various networkmonitoring technologies or routing protocols. The Route Manager can thenselect routes that correspond to a selected performance level for thevirtual network and send these routes to the computing nodes. Forexample, network W 310 and Y 312 can be built on fiber optic lines whilenetwork Y 314 and Z 316 are built on regular copper wire. The RouteManager can receive network metrics data and determine that the opticallines are faster than the copper wires (or an administrator candesignate the optical lines as a faster path). Thus, the Route Manager,in generating a route between node A 302 and node C 306 for “fast” VN1traffic, would select a path going through network W and Y (e.g., pathA-B-C).

In another situation, where the user for VN2 is not entitled to a higherservice level, VN2 traffic from node A 302 to node B 306 can be assignedto a “slow” or default path through network Y 314 and Z 316 (e.g. pathA-D-C). In order to track routing assignments, the Routing Manager canmaintain the routes and/or route association in a data store, such as aRouting Information Base (RIB) or routing table 350. The Route Managercan also track the target performance criteria 351 associated with aparticular virtual network.

In order to direct network traffic on the substrate network 300, theRouting Manager 336 can create forwarding entries for one or more of theCommunication Manager modules 320, 322, 324, 326 that direct how networktraffic is routed by the Communication Manager. The CommunicationManager modules can store those entries in forwarding tables 352, 354,356, or other similar data structure, associated with a CommunicationManager. For example, for VN1, the Route Manager can generate a controlsignal or message, such as a forwarding entry 358, that directs VN1traffic received or generated on node A 302 through network W 310 (onpath A-B-C). Meanwhile, for VN2, the Route Manager can generate acontrol signal or message, such as a forwarding entry 360, which directstraffic received on node A through network Z. The Route Manager can sendthese forwarding entries to the node A Communication Manager 320, whichcan store them on its forwarding table 352. Thus, network trafficassociated with VN1 and VN2, destined for node C 306 received orgenerated on node A can travel by either path A-B-C or path A-D-C basedon the designated performance level for VN1 and VN2.

While the example of FIG. 3 depicts only two virtual networks, the RouteManager 336 can similarly generate and maintain routes for any number ofvirtual networks. Likewise, the substrate network 300 can include anynumber of computing nodes and/or physical network devices. Routes can bedetermined based on multiple performance criteria, such as networkbandwidth, network security, network latency and network reliability.For example, traffic for a virtual network suspected of being used forspamming (e.g. mass advertisement emailing) can be routed throughnetwork filters and scanners in order to reduce spam.

FIGS. 4A and 4B illustrate a virtual network 401 and correspondingsubstrate network 402 where substrate routing is independentlydetermined from virtual routing. FIG. 4A illustrates a virtual networkincluding several virtual network components. Virtual computing nodes I4404 and I5 406 are connected to a logical router 408. The logical routercan implement certain of the features described in the logical router270 a, 270 b of FIG. 2. The logical router is connected to firewalls I1410 and I2 412. The logical router is configured to direct traffic fromI5 to I2 and I4 to I2, as would be the case if I2 were a backupfirewall. The forwarding table associated with logical router 409reflects this traffic configuration. I1 and I2 are connected to a secondrouter 414. The second router is connected to another virtual computingnode, I3 415. Thus, based on the topology and associated forwardingtable of the virtual network 401, traffic from I4 and I5 to I3 passedthrough I2.

FIG. 4B illustrates an example topology of the substrate network 402associated with the virtual network 401. The substrate network includescomputing node A 420, computing node B and a Route Manager 424.Substrate nodes A and B are each associated with a Communication Manager426, 428. Node A is simulating the operation of virtual components I2,I3 and I5 while Node B is simulating the operation of virtual componentson I1 and I4 on their respective virtual machines. The Route Manager canthen use information regarding the assignments of virtual components tocomputing nodes to optimize or otherwise adjust routing tables for thesubstrate network. The Route Manager can receive such information fromthe Communication Managers and/or the System Manager. For example,assuming I1 and I2 are identical virtual firewalls, the Route Managercan determine that because I5 and I2 are located on the same computingnode, while I4 and I1 are located on the other node, virtual networktraffic can be routed from I5 to I2 and from I4 to I1 without leavingthe respective computing node, thus reducing traffic on the network.Such a configuration is reflected in the illustrated forwarding tables430, 432 associated with the Communication Managers. Thus, routes on thesubstrate network can be determined independently of virtual networkroutes.

In some embodiments, the Route Manager 424 or System Manager canoptimize or otherwise improve network traffic using other techniques.For example, with reference to FIGS. 4A and 4B, another instance of I3can be operated on node B 422, in addition to the instance of I3 on nodeA. Thus, virtual network traffic from I5-I2-I3 and I4-I1-I3 can remainon the same computing node without having to send traffic betweencomputing nodes A and B. In one embodiment, substrate traffic can beoptimized or otherwise improved without having different forwardingentries on the substrate and the virtual network. For example, withreference to FIG. 4B, I4 can be moved from computing node B 422 to nodeA 420, thus allowing virtual traffic from I5 and I4 to I2 to remain onthe same computing node. In this way, a user monitoring traffic onlogical router 408 would see that traffic is flowing according theforwarding table in the router, that is, substrate routing istransparent to the user. Other techniques for optimizing traffic bychanging the association of virtual components with virtual machinesand/or duplicating components can also be used.

In some situations, it can be desired that substrate routes reflectroutes specified in the virtual table. For example, the virtual networkuser can wish to control how traffic is routed in the substrate network.However, rather than giving the user access to the substrate network,which could put other users at risk or otherwise compromise security, adata center operator can propagate network configuration or virtualnetwork characteristics specified by the user for the virtual network tothe substrate network. This propagated data can be used in generatingrouting paths in the substrate network, thus allowing the user to affectsubstrate routing without exposing the substrate layer to the user.

Route Selection on Overlay/Virtual Network

FIGS. 5A and 5B illustrate a virtual route selection propagated to thesubstrate network. FIG. 5A illustrates a virtual network topology wherelogical network 1 (LN1) 502 is connected to logical network 2 (LN2) 504and logical network 3 (LN3) 506 by a logical router 508. The currentpreferred routing path specified by the user is from LN1 to LN2.

A user may wish to specify a route for various reasons. For example,routing costs through LN2 can be cheaper than LN3, such as when LN2 andLN3 are in different locations with different ISPs and one ISP chargeslower rates than another. In another example, LN3 can be a backupvirtual network for LN2, and used only in some situations, such as forhandling overflow from LN2.

Referring back to FIG. 5A, the user can specify preferred routes throughthe virtual network and/or characteristics or costs associated with thevirtual components, such as monetary costs, packet loss rates,reliability rate, and/or other metrics. These characteristics can beassigned to the virtual components, such as the virtual computing nodes,node links, logical routers/switches or the like. The Route Manager 510can then determine routing tables 512 and/or forwarding tables 514 forthe virtual network.

FIG. 5B illustrates an example of a substrate route that can correspondto the virtual route in FIG. 5A. In the figure, there are three datacenters 520, 522, 524 corresponding to the logical networks 502, 504,506 of FIG. 5A. In data center 1 (DC1), a computing node 526 isconnected to a network translation device A (NTD A) 528 and a networktranslation device B (NTD B) 530. The network translation devices areconnected to external networks C 532 and D 534, respectively.

The network translation devices can serve as a gateway or entry/exitpoint into the virtual network. In some embodiments, the networktranslation devices can translate between a first addressing protocoland a second addressing protocol. For example, if the virtual network isusing IPv6 and the external networks are using IPv4, the networktranslation devices can translate from one addressing protocol to theother for traffic in either direction. In one embodiment, users connectfrom their private networks to the data centers via a VPN or otherconnection to a network translation device, which translates and/orfilters the traffic between networks.

Referring back to FIG. 5B, network C 532 connects data center 2 522 toNTD A 528. Network D 534 connects data center 3 524 to NTD B 530. TheRoute Manager module 510 is in communication with data center 1 520,data center 2 522, and data center 3 524, particularly with theCommunication Manager for the computing node 526.

From information associated with the virtual network, the Route Manager510 can determine that the user wants to route traffic from LN1 to LN2.The Route Manager can then “favor” substrate routes associated with theLN1 to LN2 virtual path. For example, the Route Manager can specify alow routing cost (e.g. cost 1) for communications, such as data packets,travelling on Network C relative to Network D (e.g. cost 10) such thatduring route determination, routes through Network C are favored. In oneembodiment, the Route Manager can apply a coefficient to storedsubstrate costs in order to favor one route over another. In anotherexample, explicit routing paths can be set up corresponding to thevirtual route. The Route Manager can identify routes in its routingtable and communicate those routes with one or more CommunicationManagers.

Referring back to FIG. 5B, when the computing node 526 receives orgenerates a packet destined for LN2 or a network reachable from LN2, thecomputing node can be configured by the Route Manager to send packetsthrough NTD A 528 as it lies on the route including network C 532.

By propagating virtual network configuration data to the substrate, andusing that configuration data in substrate route calculation, amechanism is provided for a virtual network user to affect substraterouting. In some embodiments, the virtual configuration data can be usedin determining association of the virtual components with the substratecomponents. For example, components of the same virtual network can beassociated with the same substrate computing node or on computing nodesconnected to the same switch in order to minimize or otherwise improvesubstrate network traffic. Configuration data can also be provided theother way and, in some embodiments, the user and/or virtual network canbe provided with additional substrate information, such ascharacteristics of the underlying associated substrate components (e.g.performance, costs) in order to make more informed routing decisions.

FIG. 6 illustrates an example substrate network wherein a networktranslation device determines routes into or out of a virtual network.In FIG. 6, a communication, such as a data packet, leaves computing nodeA, which is associated with a virtual network, through NTD B 604. Thenetwork translation device can include a Route Determination module 605for determining the packet route. NTD B is connected to network C 606and network D 608.

In FIG. 6, the Route Manager 610 receives a network configuration ordetermines that route A-B-C is preferred or has a cheaper cost. TheRoute Manager can store the route in a routing table 612. The RouteManager can then send forwarding entries to the NTD B 604 that configureit to send traffic through network C 606. NTD B can contain multipleforwarding entries for multiple virtual networks, such that data for onevirtual network can be sent through network C, while another virtualnetwork sends data through network D. In some cases, network packetswith the same source and/or destination are sent by different networksbased on the associated virtual network.

In some embodiments, the substrate component may not have aCommunication Manager or a Route Determination module and other ways ofcoordinating routing can be used. For example, a substrate component,such as an ordinary router or a network translation device, can be setup multiply on separate paths. Using blacklists, network traffic for aparticular virtual network can be allowed on one path but blocked onothers. The Route Manager can send a control signal or message updatingthe blacklists to manage the data flow.

In other embodiments, substrate components can implement IP aliasing,where, for example, “fast” path packets use one set of IP addresses,while “slow” path packets use another set of IP addresses. When thesubstrate component receives the packet, it can determine which path touse based on the IP address. The Route Manager can send a control signalor message to assign IP addresses to the components based on the type oftraffic handled.

Other ways of differentiating how packets are handled by substratecomponents include: tagging of packets, such as by Multiprotocol LabelSwitching (MALS); MAC stacking where a packet could have multiple MACaddresses, the first MAC address for a substrate component, such as aswitch, and a second MAC address for a next component either on the“fast” or the “slow” path; and using Network Address Translation (NAT)devices on both ends of a network in order to redirect traffic into thenetwork, such as by spoofing or altering an destination address for anincoming packing and/or altering an the source address of an outgoingpacket. In some embodiments, the Route Manager generates control signalsor messages for coordinating traffic on the substrate network for thevarious techniques described above.

Virtual Network Route Selection Process

FIG. 7A illustrates a flow diagram for a process 700 of propagatingvirtual routes to a substrate network usable in the example networksdescribed above. The virtual routes can be based on networkconfiguration data provided by a virtual network user, such as costs,component characteristics, preferred routes and/or the like.

At block 705, the Route Manager module receives user configurationand/or network configuration data, such as, for example, policy basedrouting decisions made by the user. In some embodiments, a userinterface is provided, allowing a user to specify configuration data.The Route Manager can receive the configuration data from a data store,for example, if user configuration and/or network configuration data arestored on the data store after being received on the user interface orotherwise generated. In some embodiments, the configuration data caninclude explicit routing paths through the virtual network. In someembodiments, the configuration data can specify associated costs fortraversing components of the virtual network, such as links and/ornodes. These costs can be based on monetary costs, packet loss rates,reliability rate and/or other metrics. These costs can be provided bythe user to configure the virtual network provided by the data centeroperator. However, costs and other network configuration data can comefrom the data center operator themselves in addition to or instead offrom the user. For example, the data center operator can use the virtualnetwork to provide feedback to the user on routing costs, such as byassociating monetary use costs for the substrate computing nodes and/orcomponents. In one example, the data center operator can specify a highcost for a high speed network link or high powered computing node sothat the virtual network user can take into account that cost inconfiguring the virtual network.

At block 710, the Route Manager module determines virtual network routesbased on the user configuration and/or network configuration data. Insome embodiments, routing protocols or the route determinationalgorithms of the routing protocols, such as BGP, OSPF, RIP, EIGRP orthe like, can be used to determine virtual routes.

At block 715, the Route Manager determines one or more forwardingentries for substrate network components, such as computing nodes,network translation devices, or the like. As the Route Manager candetermine routing paths and propagate routing decisions to the substratecomponents, the Route Manager can coordinate routing within a datacenter and/or between multiple data centers.

At block 720, the Route Manager transmits the forwarding entries to thesubstrate components. At block 725, the substrate component receives theforwarding entries. The substrate network components can store theforwarding entries in FIB tables or similar structures. Generally, aCommunication Manager on the substrate component receives and processesthe forwarding entry and manages communications of the substratecomponent.

However, as discussed above, network traffic can also be coordinated forsubstrate components without a Communication Manager using instead, forexample, a NAT device or the like. In some embodiments, the RouteManager can send blacklist updates, manage tagging of the packets,generate stacked MAC addresses, or the like.

At block 730, the substrate components route packets received orgenerated according to the stored forwarding entries. Generally, aCommunication Manager on the substrate component manages the packetrouting and refers to the forwarding entries to make forwardingdecisions.

Substrate Network Route Selection Process

FIG. 7B illustrates a flow-diagram for a process 750 for determiningsubstrate routing based on target performance characteristics of theassociated virtual network usable in the example networks describedabove. In some instances, the Route Manager can optionally generate avirtual routing table for the virtual network before determiningsubstrate routing. The virtual routing table can be used to determinevirtual routing paths, allowing optimization of network traffic byselective association of the virtual network components with substratecomputing nodes, such as by taking into account physical location andvirtual network traffic patterns. However, generation of the virtualrouting table is not necessary as the substrate routes can be determinedindependently of the virtual routes, as will be described below. Inaddition, user configuration and/or network configuration data providedby the user can be used to describe the virtual network, without needingto generate a virtual routing table.

At block 755, the Route Manager receives characteristics of thesubstrate nodes and/or node links. The Route Manager can receive thecharacteristics data from a data store. In some embodiments, a userinterface is provided, allowing a user to specify characteristics data.The characteristics can describe such things as monetary costs, networkbandwidth, network security, network latency, network reliability and/orthe like. These characteristics can be used in a cost function fordetermining substrate routing paths. This information can be kept by theRoute Manager or data source accessible by the Route Manager.

At block 760, the Route Manager receives a target network performancefor the virtual network. The target performance can be based on apurchased service level by the user, user history, security data or thelike. For example, a service level purchased by a user can have minimumbandwidth, latency or quality of service requirements. In anotherexample, a user can be a new customer with an unknown payment historysuch that the user is provisioned on a “slow” virtual network in orderto minimize incurred expenses in case the user fails to pay. In anotherexample, a user identified as carrying dangerous or prohibited traffic,such as viruses, spam or the like, can be quarantined to particularsubstrate components. During quarantine, the virtual network componentscan be assigned to specialized substrate components with more robustsecurity features. For example, the substrate components can haveadditional monitoring functionally, such as a deep-packet scanningability, or have limited connectivity from the rest of the substratenetwork.

At block 765, the Route Manager determines substrate network routesbased on the target network performance and/or characteristics of thesubstrate nodes and/or links. In one embodiment, the Route Manager canuse the characteristic data in a cost function for determining routes.Which characteristic to use or what level of service to provide can bedetermined by the performance criteria or target performance. Forexample, for a “fast” route, the Route Manager can use bandwidth and/orlatency data for the substrate network to generate routes that minimizelatency, maximize available bandwidth, and/or otherwise improve networkperformance.

The Route Manager can re-determine routes as needed based on changes inthe network, the configuration data and/or the performance level. Forexample, if a user has purchased N gigabits of “fast” routing but hasreached the limit, the Route Manager can generate new routes and shiftthe user to “slow” routing.

At block 770, the Route Manager transmits forwarding entries for one ormore routes to one or more nodes and/or network translation devices. Insome embodiments, the Route Manager determines forwarding entries forthe substrate components and sends those forwarding entries to thesubstrate components on the path. In some embodiments, the Route Managercan send blacklist updates, manage tagging of data packets and/orgenerate stacked MAC addresses.

At block 775, the Route Manager can optionally update the virtualrouting table based on substrate network routes. By changing the virtualnetwork routing table based on the substrate routes, the virtual networkcan stay logically consistent with the behavior of the substratenetwork. Thus, users won't necessarily be confused by discrepancies inthe virtual routing.

Source-Dependent Address Resolution

With reference now to FIGS. 8-11, various embodiments for theimplementing and managing source-dependent address resolution will bedescribed. As previously described, the substrate network 100 includes anumber of physical computing systems 105 that host one or more virtualmachine instances 107 (FIG. 1). As will be explained in greater detail,the number of virtual machine instances hosted on each physicalcomputing system 105 can vary according to the computing deviceresources associated with each individual physical computing system 105and in accordance with the management policies of the substrate network100. As previously described, the substrate network 100 also includes avirtual machine manager component, such as ONM system manager 110, formanaging the allocation of virtual machine instances 107 on the variousphysical computing systems 105. In one embodiment, the hosted virtualmachine instances can be configured in a manner to logically represent anetwork of virtual machine instances, generally referred to as a hostedvirtual machine network.

With reference to FIG. 8, a simplified block diagram of the substratenetwork 100 of FIG. 1 will be described as illustrating interactionsbetween various components of the substrate network for the purposes ofsource-dependent address resolution. However, one skilled in therelevant art will appreciate that illustrative interaction andcommunications may include, or otherwise involve, additional componentsnot illustrated in the figures.

The simplified substrate network 100 includes a number of components forfacilitating source-dependent address resolution, including a resourceallocation component 850, a port association data store 852, asource-dependent address resolution component 860, and an addressresolution data store 862, each of which will be described in moredetail below. In addition, the simplified substrate network 100 includesone or more physical computing devices 802 hosting a number of virtualcomputing devices 814, 816, 824 and 826. The virtual computing devices814, 816, 824 and 826 may be hosted by a single physical computingdevice or by multiple physical computing devices in communication viathe network 840. Network 840 may correspond to any wired or wirelessnetwork (or combination thereof) facilitating communication between theone or more physical computing devices 802, the resource allocationcomponent 850, the port association data store 852, the source-dependentaddress resolution component 860, and the address resolution data store862.

In FIG. 8, virtual computing devices 814, 816, 824 and 826 areassociated into two hosted virtual machine networks 810 and 820.Specifically, hosted virtual machine network 810 can include any numberof hosted virtual computing devices, including virtual computing device‘A’ 814 and virtual computing device ‘B’ 816. Hosted virtual machinenetwork 830 can include any number of hosted virtual computing devices,including virtual computing device ‘X’ 824 and virtual computing device‘Y’ 826. Each hosted virtual machine network 810 and 820 may enablecommunication between virtual computing devices within the hostedvirtual machine network 810 or 820, respectively, as well as othercomputing devices (virtual or physical) external to the hosted virtualmachine network 810 or 820. Illustratively, the range of networkaddresses utilized to facilitate the exchange of data between virtualnetwork components associated with a common hosted virtual network canbe arbitrarily selected without regard to the network addressesassociated with the physical computing devices hosting the componentsand independent of network addresses associated with other hostedvirtual networks. In some embodiments, communication with externalcomputing devices may be facilitated in whole or in part by a peeringgateway, such as peering gateways 818 and 828. Each peering gateway 818and 828 may enable communication with a respective hosted virtualmachine network 810 or 820 via an external addressing scheme.

For purposes of an illustrative example, each of the hosted virtualmachine networks 810 may be associated with an internal address range of192.168.1.0/24, as shown in FIG. 8. Because the hosted virtual machinenetworks 810 and 820 are distinct, overlapping network ranges may besupported. However, overlapping network ranges are not required withinthe context of the current disclosure. Each virtual computing device814, 816, 824 and 826 is associated with an internal network addresswithin the above-noted internal address range. For example, virtualcomputing device ‘A’ 814 is associated with an internal address of192.168.1.101. Similarly, virtual computing device ‘B’ 816 is associatedwith an internal address of 192.168.1.102. By addressing networkcommunication to these internal addresses, the virtual computing deviceswithin the common hosted virtual machine network 810 can exchangeinformation utilizing the internal address identifiers.

However, because each of the hosted virtual machine networks 810 and 820are distinct, computing devices external to the hosted virtual machinenetwork 810 may not address virtual computing devices 814 and 816 by useof the internal addresses above. Accordingly, virtual computing devices814 and 816 may also be associated with external network addresses203.0.113.50 and 203.0.113.51, respectively. Each of these addresses mayenable communication with computing devices external to the hostedvirtual machine network 810. In some embodiments, this externalcommunication may be facilitated by the peering gateway 818. Forexample, the peering gateway 818 may be configured to receivecommunication addressed to an eternal network address, and to forwardthe communications to an appropriate internal network address.

In accordance with common network protocols, each virtual computingdevice 814, 816, 824 and 826 may be associated with an identifier, suchas a network name. Network names may be human-readable (or substantiallyhuman-readable) identifiers assigned to a computing device based on ahuman-created naming schema. For example, the virtual computing device A814 may be associated with the address name ‘CDA.802.HCN.TLD’ (e.g.,indicating the name identifies computing device A of network 810 withina hosted computing network). Virtual computing devices 816, 824 and 826may be identified as shown in FIG. 8. Each network name may enablecommunication with other computing devices (e.g., internal or externalto a given hosted virtual machine network) by use of a DNS server, thatincludes a source-dependent address resolution component as describedbelow. Illustratively, a DNS server obtains a DNS query including theidentification of a network name. The DNS server then typically resolvesthe DNS query by returning one or more network addresses thatcorresponds to the network name. As will be described, the DNS servercan vary the network address that is returned by determining whether theDNS query was transmitted by a virtual computing device associated witha common hosted virtual network component.

Internal network addresses, external network address, networkidentifiers, or any combination thereof may be associated with virtualcomputing devices 814, 816, 824 and 826 by interaction with the resourceallocation component 850. Specifically, the resource allocationcomponent 850 may be configured to receive a request from a physicalcomputing device 802 to allocate network resources to a hosted virtualcomputing device. For example, a physical computing device 802 mayattempt to instantiate a new virtual computing device, and may requestallocate of network resources for the virtual computing device from theresource allocation component 850. The resource allocation component maydetermine available network resources (e.g., available internaladdresses, external addresses or identifiers) and return suchinformation to the physical computing device 802. Thereafter, the newlyinstantiated virtual computing device may be configured to conform tothe allocated network resources.

In some embodiments, any one or more of internal addresses, externaladdresses, or network identifiers may be assigned to virtual computingdevices without use of the resource allocation component 850. Forexample, in one embodiment, the resource allocation component 850 may beconfigured to allocate external addresses, but to allow individualvirtual computing devices or hosted virtual machine networks to allocateinternal addresses. In another embodiment, the resource allocationcomponent 850 may be configured to allocate a portion of a networkidentifier (e.g., a trailing portion), while enabling a virtualcomputing device or hosted virtual machine network to specify aremainder of the network identifier (e.g., a leading portion).Allocations of internal addresses, external address and networkidentifiers may be stored within the address resolution data store 862.The address resolution data store 862 may correspond to any persistentor substantially persistent data storage, such as a hard drive (HDD), asolid state drive (SDD), network attached storage (NAS), a tape drive,or any combination thereof. In some embodiments, the port addressresolution data store 862 may comprise a distributed collection ofstorage devices. For example, where a large number of hosted virtualmachine networks (not shown in FIG. 8) are hosted within the substratenetwork 100, multiple resource allocation components 850 and addressresolution data store 862 may be provided. Each resource allocationcomponent 850 and address resolution data store 862 may be incommunication via the network 840, and may be synchronized accordinglyto a number of synchronization techniques known in the art.

As will be discussed in more detail below, the resource allocationcomponent 850 may also be configured to allocate an address resolutionsource port to one or more of the virtual computing devices 814, 816,824 and 826. Specifically, the resource allocation component 850 mayallocate a distinct address resolution source port to each virtualcomputing device hosted by a common physical computing device 802. Aswill be described below, each of the virtual computing devices 814, 816,824 and 826 may be configured to transmit address resolution requests tothe source-dependent address resolution component via a physicalcomputing device 802. Because such address resolution requests aretransmitted via a physical computing device 802, they may appear to thesource-dependent address resolution component 860 to originate at thephysical computing device 802. However, by assigning a unique addressresolution source port to each virtual computing device hosted by asingle physical computing device 802, an originating virtual computingdevice for an address resolution request may be determined. Associationsbetween virtual computing devices 814, 816, 824 and 826 and source-portsmay be stored within the port association data store 852. Similarly tothe address resolution data store 862 discussed above, the portassociation data store 852 may correspond to any persistent orsubstantially persistent data storage, such as a hard drive (HDD), asolid state drive (SDD), network attached storage (NAS), a tape drive,or any combination thereof. In some embodiments, the port associationdata store 852 may comprise a distributed collection of storage devices.

In addition, the substrate network 100 may include one or more DNSsevers having a source-dependent address resolution component 860, oraccess to such a component or service. The source-dependent addressresolution component 860 can, among other things, be configured toreceive requests for address resolution from a virtual computing device814, 816, 824 or 826 (or any other computing device), and to return anetwork address of a targeted computing device. For example, an addressresolution request may correspond to a request for the network addressof the virtual computing device A 814, identified as “CDA.810.HCN.TLD.”The source-dependent address resolution component 860 may be configuredto determine a network from which the request was received (e.g., asource network), and to return an internal or external address of thevirtual computing device A 814 based on such a source network.Specifically, if the source network corresponds to hosted virtualmachine network 810 (containing virtual computing device A 814), thesource-dependent address resolution component 860 may return theinternal address of virtual computing device A 814, 192.168.1.101.However, if the source network does not correspond to hosted virtualmachine network 810 (containing virtual computing device A 814), thesource-dependent address resolution component 860 may return theexternal address of virtual computing device A, 203.0.113.50. In thismanner, computing devices internal to the hosted virtual machine network810 may communicate directly to the virtual computing device A 814,without requiring interaction with the peering gateway 818. Such directcommunication may reduce the network resources required to communicatewith the virtual computing device A 814. Similarly, computing devicesexternal to the hosted virtual machine network 810 may communicate tothe virtual computing device A 814 via the peering gateway 818. Suchindirect communication may maintain the security and anonymity ofcomputing devices within the hosted virtual machine network 810.

In some embodiments, the source-dependent address resolution component860 may be included within a modified version of a standard DNScomponent. For example, a typical DNS server may be configured toreceive requests for an address corresponding to a given name, and toreturn the requested address. However, a typical DNS server may not beconfigured to generate a response based on a source address, but insteadmay be configured to return the same address regardless of the source ofthe request. Accordingly, in some embodiments, a typical DNS server maybe modified to include a source-dependent address resolution component860 as discussed herein. For example, in one embodiment, thesource-dependent address resolution component 860 may be included as asoftware module within a computing device implementing the PowerDNS™service.

In addition, in some instances, typical DNS components may be configuredto cache address resolution information in order to provide subsequentrapid access to such information. However, standard caches providedwithin a DNS component may be insufficient to provide source-dependentaddress resolution in accordance with embodiments of the presentdisclosure. Specifically, standard DNS caches may associate a frequentlyrequested identifier (e.g., a network name) of a computing device with aspecific network address of the computing device. However, as will bediscussed below, where source-dependent address resolution isimplemented, an identifier of a computing device may be associated withmultiple network addresses of the computing device (e.g., an internaland an external network address). Accordingly, caches associating anidentifier with a single network address might be insufficient forproviding source-based address resolution. In some embodiments, cachesassociated with typical DNS components may be disabled, in order toprevent potential errors when providing source-dependent addressresolution. For example, each request for address resolution may beprocessed by the source-dependent address resolution componentindependently, without regard to address resolution r previouslydetermined by the source-dependent address resolution component. Inother embodiments, caches associated with typical DNS components may beenabled only for certain DNS requests (e.g., those wheresource-dependent address resolution is not required). In still moreembodiments, caches associated with typical DNS components may bemodified, such that the cache includes associations between a requestedidentifier (e.g., a network name) of a computing device, an identifierof a source computing device (or source network containing the sourcecomputing device), and a specific network address of the computingdevice. In this regard, a modified cache may provide rapid subsequentaccess to address resolution information associated with a requestingsource computing device (or source network containing the sourcecomputing device).

In some embodiments, in order to facilitate a large number ofsource-dependent address resolution requests without traditional cachingtechniques (or with use of modified caching techniques described above),multiple source-dependent address resolution components 860 may beprovided. For example, a collection of source-dependent addressresolution components 860 may function to cooperatively service addressresolution requests from a plurality of computing devices. To ensureconsistency, the source-dependent address resolution components 860 maysynchronize address resolution information according to a number ofknown synchronization techniques. In another embodiment, asource-dependent address resolution component 860 may be implemented bya number of computing devices, such as within a distributed computingenvironment. For example, a source-dependent address resolutioncomponent 860 may be implemented by a number of computing devices(physical or virtual) in communication with the network 840.

In addition, some DNS systems may include “split-horizon” or“split-view” DNS, which may provide different sets of DNS informationbased on a source of address of the DNS request. However, such systemsare generally limited to a fixed number of “views,” or associationsbetween DNS information and specific sources. Accordingly, suchsplit-view DNS systems are generally insufficient to provide a largeamount of diverse source-dependent address resolution to a large numberof computing devices. In addition, where multiple virtual computingdevices are hosted within a single physical computing device, atraditional split-view DNS may recognize all requests of the virtualcomputing devices as originating from the physical computing device.Because split-view DNS systems may determine a target address based on asource address of a request, the split-view DNS systems may therefore beunable to provide distinct DNS information to multiple virtual computingdevices hosted within the same physical computing device. Still further,while split-view DNS systems may provide distinct DNS information todifferent requesting computing devices, such split-view DNS systems maynot be capable of intelligently determining whether a requestingcomputing device is within the same internal network as a targetcomputing device. Accordingly, a typical split-view DNS system may beunable to intelligently provide internal or external addresses based onsuch a determination. Embodiments of the present disclosure thereforerepresent a number of advantages over traditional split-view DNSsystems.

With reference to FIG. 9, one illustrative interaction for theallocation of network resources (e.g., an internal address, externaladdress, identifier, or combination thereof) as well as allocation of asource-port to a virtual computing device, such as virtual computingdevice A 814 of FIG. 8 will be described. For the purposes of FIG. 9, itwill be assumed that the virtual computing device A 814 has beenassigned an internal network address (e.g., by an administrator of thevirtual computing device A 814), but has not yet been assigned anexternal network address or a resolvable network identifier (e.g., anetwork name). The interactions of FIG. 9 may occur, for example,immediately or substantially immediately after launching orinstantiating the virtual computing device A 814 on the physicalcomputing device 802.

As shown in FIG. 9, at (1), the virtual computing device A 814 (or thephysical computing device 802 on behalf of the virtual computing deviceA 814) may transmit a request for network interface information to theresource allocation component 850. The request may correspond to any ofa number of known protocols. For example, in one embodiment, the requestmay comprise to a DHCP request. After receiving the request, theresource allocation component 850 may determine appropriate networkinterface information (e.g., an external address and a network name) toallocate to the physical computing device A 814.

In addition, the resource allocation component 850 may determine anappropriate source port to assign to the virtual computing device A 814for purposes of source-dependent address resolution services.Specifically, at (2), the resource allocation component 850 may requesta set of current port associations from the port association data store852. Current port associations may correspond to any previously existingassociation between source ports and virtual computing devices. Suchcurrent port associations may be returned to the resource allocationcomponent 850 at (3).

Thereafter, the resource allocation component 850 may determine a newport association to assign to the virtual computing device A 814. Asnoted above, source ports may be associated with virtual computingdevices such that each virtual computing device hosted by an individualphysical computing device is assigned a unique source port. For example,where the virtual computing device A 814 is hosted by the same physicalcomputing device 802 as another virtual computing device, each of thevirtual computing devices may be assigned distinct source ports.However, where the virtual computing device A 814 is hosted by adifferent physical computing device 802 than another virtual computingdevice, these virtual computing devices may be assigned the same sourceport. Specifically, because the different hosting physical computingdevices 802 are each associated with a different network address,address resolution requests may be differentiated based on the networkaddress of the physical computing device, rather than on the sourceport. However, where the same physical computing devices 802 hostsmultiple virtual computing devices, network address may not be possiblebased solely on a network address of the physical computing device 802.Accordingly, the resource allocation component 850 may, at (4),determine a source port to assign to the virtual computing device A 814such that a combination of the network address of the physical computingdevice 802 and the determined source port is unique. At (5), the newlydetermined port association may be transmitted to the port associationdata store 852 for storage, such that the port associations containedtherein are updated for future use.

Prior to, simultaneously with, or after determination of a source port,the resource allocation component 850 may, at (6), allocate additionalnetwork interface information (e.g., an external address or networkname) to the virtual computing device A 814. Allocation of networkaddresses and names is generally known within the art, and thereforewill not be discussed in greater detail herein.

Thereafter, at (7), the allocated network interface information (e.g.,an external address or network name) as well as the source portassociation information may be returned to the virtual computing deviceA 814. Thereafter, the virtual computing device A 814 (or the physicalcomputing device 802 on behalf of the virtual computing device A 814)may utilize the returned information to cause future address resolutionrequests to be transmitted from the assigned source port.

In addition, at (8), the resource allocation component 850 may transmitthe network interface information to the address resolution data store862. For example, the resource allocation component 850 may update theinformation within the address resolution data store 862 to reflect thatvirtual computing device A 814 is associated with an assigned externaladdress, network name, or both.

With reference now to FIGS. 10A and 10B, illustrative interactionsdepicting the fulfillment of an address resolution request based atleast in part on a source of the request will be described.Specifically, FIG. 10A depicts the fulfillment of request for addressresolution where the target virtual computing device and the sourcevirtual computing device are within the same hosted virtual machinenetwork. FIG. 10B, in turn, depicts the fulfillment of request foraddress resolution where the target virtual computing device and thesource virtual computing device are within different hosted virtualmachine networks.

In FIG. 10A, an address resolution request for the virtual computingdevice A 814 of FIG. 8 (not shown in FIG. 10A) is depicted. The addressresolution request is transmitted by the virtual computing device B 816.As shown in FIG. 8, both the target virtual computing device A 814 andthe source virtual computing device B 816 are part of the hosted virtualmachine network 810. Accordingly, the target virtual computing device A814 and the source virtual computing device B 816 are enabled tocommunicate by use of internal network addresses. However, in order toensure flexibility in networking, security, and human readability, thevirtual computing device B 816 may not be constantly aware of theinternal address of virtual computing device A 814. Instead, the virtualcomputing device B 816 may maintain an identifier of the virtualcomputing device A 814 (e.g., a network name) Such an identifier may beresolvable to a network address of the virtual computing device A 814 byuse of an address resolution component, such as the source-dependentaddress resolution component 860.

Accordingly, at (1), the virtual computing device B 816 may transmit arequest for address resolution to the source-dependent addressresolution component 860. The request may include the identifier of thevirtual computing device A 814 (e.g., “CDA.810.HCN.TLD”). The requestmay be transmitted (e.g., via network 840 of FIG. 8) from a physicalcomputing device 802 on behalf of the virtual computing device B 816.Because the request may appear to originate on the physical computingdevice 802, the request may not be identifiable to the resourceallocation component 850 as originating at the virtual computing deviceB 816. Accordingly, the virtual computing device B 816 (or the physicalcomputing device 802 on behalf of the virtual computing device B 816)may transmit the request on a designated source port associated with thevirtual computing device A 814. For example, the virtual computingdevice B 816 may have previously been associated with source port 8004(e.g., via the interactions of FIG. 9). The source-dependent addressresolution component 860 may therefore receive the request asoriginating from the physical computing device 802 on source port 8004.

Thereafter, the source-dependent address resolution component 860 maydetermine a source network (e.g., a hosted virtual machine network) fromwhich the request originated. Specifically, at (2), the source-dependentaddress resolution component 860 may query the port association datastore 852 as to the source network. In some instances, the portassociation data store 852 may contain information as to associationsbetween specific source port and source address combinations, and a truesource of the request. For example, the port association data store 852may contain information indicating that, for a request from the physicalcomputing device 802 on port 8004, the virtual computing device B 816 isthe true source of the request. A source identifier of this source maybe returned to the source-dependent address resolution component 860 at(3). The source-dependent address resolution component 860 maythereafter determine, based on the source identifier, a source networkof the request. Specifically, the source-dependent address resolutioncomponent 860 may determine that, because virtual computing device B 816is part of the hosted virtual machine network 810, that the hostedvirtual machine network 810 corresponds to the source network. In otherembodiments, the port association data store 852 may contain informationmapping specific source port and source address combinations to sourcenetworks. For example, the port association data store 852 may containinformation indicating that, for a request from the physical computingdevice 802 on port 8004, the source network is hosted virtual machinenetwork 810. An identifier of the source network may be returned to thesource-dependent address resolution component 860 at (3).

Prior to, simultaneous to, or after determining a source network of therequest, the source-dependent address resolution component 860 may alsodetermine a destination network of the request. The destination networkmay generally correspond to the hosted virtual machine network thatincludes the virtual computing device identified within the request.Specifically, at (4), the source-dependent address resolution component860 may transmit a query to the address resolution data store 862 as tothe target network including the virtual computing device A 814, asidentified within the request (e.g., by network identifier). The addressresolution data store 862 may reference the identifier within therequest in order to determine a target network. For example, in oneembodiment, the address resolution data store 862 may includeinformation mapping a specific identifier to a target network. Forexample, the address resolution data store 862 may include informationmapping identifier “CDA.810.HCN.TLD” (corresponding to virtual computingdevice A 814) to target hosted virtual machine network 810. Informationidentifying the target network may be returned at (5).

After determining a source network of the request and a target network,the source-dependent address resolution component 860 may determine anappropriate address to return to the requesting virtual computingdevice. Specifically, in instances where the source network and thetarget network are the same, an internal address may be returned(enabling communication within the shared network). In instances wherethe source and target network are different, an external address may bereturned (enabling communication across the different networks).

In the illustrative interaction of FIG. 10A, the source network and thetarget network are both determined to be hosted virtual machine network810. Accordingly, at (6), the source-dependent address resolutioncomponent 860 may query the address resolution data store 862 for theinternal address of the target device identified within the request. Forexample, the source-dependent address resolution component 860 may querythe address resolution data store 862 for the internal addresscorresponding to identifier “CDA.810.HCN.TLD” (identifying virtualcomputing device A 814). As shown in FIG. 8, the virtual computingdevice A 814 has an internal address of 192.168.1.101. Accordingly, thisinternal address may be returned to the source-dependent addressresolution component 860 at (7). The internal address may in turn bereturned to the virtual computing device B 816 at (8). Thereafter, thevirtual computing device B 816 may communicate with the target virtualcomputing device A 814 by use of internal address 192.168.1.101.

Similarly to FIG. 10A, FIG. 10B depicts the fulfillment of request foraddress of the virtual computing device A 814 of FIG. 8 (not shown inFIG. 10B). However, in FIG. 10B, the address resolution request istransmitted by the virtual computing device X 824. As shown in FIG. 8,the target virtual computing device A 814 is part of the hosted virtualmachine network 810, while the source virtual computing device X 816 ispart of the hosted virtual machine network 820. Accordingly, the targetvirtual computing device A 814 and the source virtual computing device X824 may communicate by external network addresses. The virtual computingdevice X 824 may not be constantly aware of the external address ofvirtual computing device A 814. Instead, the virtual computing device B816 may maintain an identifier of the virtual computing device A 814(e.g., a network name). Such an identifier may be resolvable to anetwork address of the virtual computing device A 814 by use of anaddress resolution component, such as the source-dependent addressresolution component 860.

Accordingly, at (1), the virtual computing device X 824 may transmit arequest for address resolution to the source-dependent addressresolution component 860. The request may include the identifier of thevirtual computing device A 814 (e.g., “CDA.810.HCN.TLD”). The requestmay be transmitted (e.g., via network 840 of FIG. 8) from a physicalcomputing device 802 on behalf of the virtual computing device A 814.Because the request may appear to originate on the physical computingdevice 802, the request may not be identifiable to the resourceallocation component 850 as originating at the virtual computing deviceX 824. Accordingly, the virtual computing device X 824 (or the physicalcomputing device 802 on behalf of the virtual computing device X 824)may transmit the request on a designated source port associated with thevirtual computing device X 824. For example, the virtual computingdevice X 824 814 may have previously been associated with source port8006 (e.g., via the interactions of FIG. 9). The source-dependentaddress resolution component 860 may therefore receive the request asoriginating from the physical computing device 802 on source port 8006.

Thereafter, the source-dependent address resolution component 860 maydetermine a source network (e.g., a hosted virtual machine network) fromwhich the request originated. Specifically, at (2), the source-dependentaddress resolution component 860 may query the port association datastore 852 as to the source network. An identifier of the source networkmay be returned to the source-dependent address resolution component 860at (3). In the illustrative interaction of FIG. 10B, the source networkmay correspond to the hosted virtual machine network 820, as shown inFIG. 8.

Prior to, simultaneous to, or after determining a source network of therequest, the source-dependent address resolution component 860 may alsodetermine a destination network of the request. Similarly to FIG. 10A,above, at (4), the source-dependent address resolution component 860 maytransmit a query to the address resolution data store 862 as to thetarget network including the virtual computing device A 814, asidentified within the request (e.g., by network identifier). At (5),information identifying the target network may be returned. In theillustrative interaction of FIG. 10B, the target network may beidentified as corresponding to the hosted virtual machine network 810,as shown in FIG. 8.

After determining a source network of the request and a target network,the source-dependent address resolution component 860 may determine anappropriate address to return to the requesting virtual computingdevice. Specifically, as noted above, in instances where the source andtarget network are different, an external address may be returned(enabling communication across the different networks). In theillustrative interaction of FIG. 10B, the source network and the targetnetwork are determined to be the hosted virtual machine networks 810 and820, respectively. Accordingly, at (6), the source-dependent addressresolution component 860 may query the address resolution data store 862for the external address of the target device identified within therequest. For example, the source-dependent address resolution component860 may query the address resolution data store 862 for the externaladdress corresponding to identifier “CDA.810.HCN.TLD” (identifyingvirtual computing device A 814). As shown in FIG. 8, the virtualcomputing device A 814 has an internal address of 203.0.113.50.Accordingly, this external address may be returned to thesource-dependent address resolution component 860 at (7). The externaladdress may in turn be returned to the virtual computing device X 824 at(8). Thereafter, the virtual computing device X 824 may communicate withthe target virtual computing device A 814 by use of external address203.0.113.50.

With reference to FIG. 11, one illustrative routine 1100 forsource-dependent fulfillment of address resolution requests will bedescribed. The routine 1100 may be carried out, for example, by thesource-dependent address resolution component 860 of FIG. 8.Specifically, at block 1102, the source-dependent address resolutioncomponent 860 may receive a request for resolution of a network addressof a virtual computing device. For example, the request may correspondto a request to resolve the network name CDX.812.HCN.TLD (correspondingto virtual computing device X 824 of FIG. 8) into an IP address.Thereafter, at block 1104, the source address and source port of therequest may be determined. As noted above, embodiments of the presentdisclosure include associating specific network address and source portcombinations with a given source network (or source virtual computingdevice associated with a source network). For example, the request mayhave originated from an address of a physical computing device 802hosting the virtual computing device B 816 of FIG. 8. The request mayhave further originated on source port 8004, previously associated withvirtual computing device B 816 (exclusively or in addition to othervirtual computing devices on other physical computing devices).Accordingly, the request may be determined to have originated fromvirtual computing device B 816.

Thereafter, at block 1106, the source-dependent address resolutioncomponent 860 may determine a source network of the request. Forexample, if the source port and source address indicate the request wasreceived from virtual computing device B 816, the source-dependentaddress resolution component 860 may determine the source network to bethe hosted virtual machine network 810. In some embodiments, thesource-dependent address resolution component 860 may identify a sourcenetwork by communication with the port association data store 852.Similarly, at block 1108, the source-dependent address resolutioncomponent 860 may determine a target network of the request. Forexample, if the request is targeted to virtual computing device X 824,as identified by network name CDX.812.HCN.TLD, the source-dependentaddress resolution component 860 may determine the target network to behosted virtual machine network 820. In some embodiments, thesource-dependent address resolution component 860 may identify a sourcenetwork by communication with the address resolution data store 862.

At block 1110, the source-dependent address resolution component 860 maydetermine whether the source network and the target network are the samevirtual hosted machine network. As discussed above, where the sourcenetwork and the target network are the same virtual hosted machinenetwork, the requesting device may communicate with the target devicevia an internal network address. However, where the source network andthe target network are not the same virtual hosted machine network,external addressing must be utilized to communicate between devices.Accordingly, if the source network and the target network are the samevirtual hosted machine network, the routine may continue at block 1116,where the source-dependent address resolution component 860 maydetermine an internal address of the target device. For example, thesource-dependent address resolution component 860 (e.g., in conjunctionwith the address resolution data store 862) may determine that networkname CDX.812.HCN.TLD (of virtual computing device X 824) corresponds tointernal address 192.168.1.101. This internal address may then bereturned to the requesting computing device at block 1118. Thereafter,the routine 1100 may end at block 1120.

However, if the source network and the target network are not the samevirtual hosted machine network, the routine may continue at block 1112,where the source-dependent address resolution component 860 maydetermine an external address of the target device. For example, thesource-dependent address resolution component 860 (e.g., in conjunctionwith the address resolution data store 862) may determine that networkname CDX.812.HCN.TLD (of virtual computing device X 824) corresponds toexternal address 203.0.113.20. This external address may then bereturned to the requesting computing device at block 1114. Thereafter,the routine 1100 may end at block 1120.

Though described above in sequence, one skilled in the art willappreciate that portions of the routine 1100 described above mayimplemented or executed simultaneously or in different order than asdescribed above. For example, in some embodiments, determination of atarget network (e.g., at block 1108) may occur prior or simultaneouslyto determination of a source network (e.g., at blocks 1104 and 1106).Accordingly, the elements of the routine 1100 are intended to beillustrative, and not limiting.

In addition, though determination of a source network is discussedherein based at least in part on a source port of a request, a sourcenetwork may alternatively or additionally be determined based on othercriteria. For example, in some embodiments, resolution requests may bemodified to include a source network or unique source addresscorresponding to a source network within the request. Illustratively,encapsulation techniques may be employed to include a source network orinformation resolvable to a source network. Accordingly, utilization ofsource-port identification techniques is intended to be illustrative,and not limiting.

Still further, while resolution of network names into network addressesis described herein, embodiments of the present disclosure may enablesource-dependent resolution of other aspects of computing devices. Forexample, in some instances, a virtual computing device may be associatedwith both an internal network name and an external network name. Aninternal network name may correspond to a human-readable (orsubstantially human readable) name resolvable to an address of thecomputing device within a specific network. An external network name maycorrespond to a human-readable (or substantially human readable) nameresolvable to an address of the computing device outside of the specificnetwork (e.g., as part of a global domain name system). In oneembodiment, internal or external network names may be resolvable basedon other identifying information of a computing device, such as anexternal address. For example, a source-dependent address resolutioncomponent may be configured to fulfill reverse address resolutionrequests received from computing devices. Specifically, where a reverseaddress resolution request is received from a computing device sharing anetwork with the target device identified in the request, an internalnetwork name may be returned. Where reverse address resolution requestis received from a computing device not sharing a network with thetarget device identified in the request, an external network name may bereturned. Accordingly, resolution of network names to network addressesis intended to be illustrative, and not limiting.

All of the processes described herein may be embodied in, and fullyautomated via, software code modules executed by one or more generalpurpose computers or processors. The code modules may be stored in anytype of computer-readable medium or other computer storage device. Someor all the methods may alternatively be embodied in specialized computerhardware. In addition, the components referred to herein may beimplemented in hardware, software, firmware or a combination thereof.

Conditional language such as, among others, “can,” “could,” “might” or“may,” unless specifically stated otherwise, are otherwise understoodwithin the context as used in general to convey that certain embodimentsinclude, while other embodiments do not include, certain features,elements and/or steps. Thus, such conditional language is not generallyintended to imply that features, elements and/or steps are in any wayrequired for one or more embodiments or that one or more embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements and/or steps are included orare to be performed in any particular embodiment.

Conjunctive language such as the phrase “at least one of X, Y and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require at least one of X, atleast one of Y and at least one of Z to each be present.

Any process descriptions, elements or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or elements in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown, or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved as would be understood by those skilled in the art.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which are to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

What is claimed is:
 1. A computer-implemented method for facilitatingsource-dependent address resolution, the computer-implemented methodcomprising: maintaining, at an address resolution system associated witha plurality of virtual computing devices, address resolution informationmapping network names of the plurality of virtual computing devices tointernal and external network addresses of the plurality of virtualcomputing devices, wherein individual virtual computing devices of theplurality of virtual computing devices are associated with both aninternal network address, which enables communication with othercomputing devices associated with a network of the individual virtualcomputing device, and an external network address, which enablescommunication with other computing devices not associated with thenetwork; receiving, at the address resolution system, a DNS queryrequest from a source virtual computing device, wherein DNS queryrequest corresponds to a request for an address of a target virtualcomputing device, and wherein the request comprises a network name ofthe target virtual computing device; identifying, at the addressresolution system and based at least in part on the received request, asource network of the source virtual computing device; identifying, atthe address resolution system and based at least in part on the receivedrequest and on the address resolution information, a target networkincluding the target virtual computing device; determining, at theaddress resolution system, whether the source network and the targetnetwork are the same network; selecting, at the address resolutionsystem, at least one of the internal address or the external address ofthe target virtual computing device for transmission to the sourcevirtual computing device, wherein the address resolution system selectsthe internal address of the target virtual computing device fortransmission to the source virtual computing device when it isdetermined that the source network and the target network are the samenetwork, and wherein the address resolution system selects the externaladdress of the target virtual computing device for transmission to thesource virtual computing device when it is determined that the sourcenetwork and the target network are not the same network; andtransmitting the selected at least one address from the addressresolution system to the source virtual computing device.
 2. Thecomputer-implemented method of claim 1, wherein determining a sourcenetwork of the source computing device is further based at least in parton an address of a physical computing device hosting the source virtualcomputing device.
 3. The computer-implemented method of claim 1, whereindetermining a source network of the source virtual computing device isfurther based at least in part on a source port from which the requestis received.
 4. The computer-implemented method of claim 1, wherein atleast one of the source network and the target network is a hostedvirtual machine network simulated by one or more physical computingdevices.
 5. The computer-implemented method of claim 1, wherein themethod is carried out independently of any previously received DNSqueries.
 6. A system for source-dependent address resolution, the systemcomprising: at least one data store storing address resolutioninformation mapping identifiers of individual computing devices, of aplurality of computing devices, to both internal and external addressesof the individual computing devices; and one or more computing devicesimplementing an address resolution system, the address resolution systemconfigured to: receive, at the address resolution system, a request forresolution of an identifier of the target computing device to an addressof the target computing device; determine, at the address resolutionsystem and based at least in part on the received request, a sourcenetwork from which the request was received; determine, at the addressresolution system and based at least in part on the received request andon the address resolution information, a target network including thetarget computing device; determine, at the address resolution system,whether the source network and the target network are the same network;and respond to the request by resolving the identifier of the targetcomputing device into at least one of an internal address or an externaladdress of the target computing device and transmitting a result ofresolving the identifier from the address resolution system to a sourcecomputing device associated with the request, wherein the addressresolution system resolves the identifier of the target computing deviceinto the internal address of the target computing device when it isdetermined that the source network and the target network are the samenetwork, and wherein the address resolution system solves the identifierof the target computing device into the external address of the targetcomputing device to the source computing device when it is determinedthat the source network and the target network are not the same network.7. The system of claim 6, wherein the source computing device isconfigured to utilize the transmitted address to communicate with thetarget computing device.
 8. The system of claim 6 further comprising aphysical computing device hosting the source computing device.
 9. Thesystem of claim 8, wherein the physical computing device is configuredto transmit requests for resolution of addresses on behalf of the sourcecomputing device from a source port of the physical computing device.10. The system of claim 8, wherein the request is received from thephysical computing device.
 11. The system of claim 8, wherein the one ormore computing devices are further configured to determine a sourcenetwork from which the request was received based at least in part on anaddress of the physical computing device.
 12. The system of claim 6,wherein the at least one data store further includes information mappingaddresses of physical computing devices and source ports of requests tosource networks.
 13. The system of claim 12, wherein the one or morecomputing devices are further configured to determine a source networkfrom which the request was received based at least in part on theinformation mapping addresses of physical computing devices and sourceports of requests to source networks.
 14. The system of claim 6, whereinat least one of the source computing device and the target computingdevice is a virtual computing device.
 15. The system of claim 6, whereinthe received request is a DNS query.
 16. The system of claim 6, whereinthe one or more computing devices correspond to a plurality of computingdevices within a distributed computing environment.
 17. Anon-transitory, computer-readable storage medium havingcomputer-executable instructions for facilitating source-dependentaddress resolution that, when executed by an address resolution system,cause the address resolution system to: receive, at the addressresolution system, a request for resolution of an identifier of a targetcomputing device to an address of the target computing device, whereinthe target computing device is associated with both an internal networkaddress and an external network address; determine, at the addressresolution system and based at least in part on the received request, asource network from which the request was received; determine, at theaddress resolution system, a target network including the targetcomputing device based at least in part on the received request and onaddress resolution information mapping the identifier of the targetcomputing device to the internal and the external address of the targetcomputing device; determine, at the address resolution system, whetherthe source network and the target network are the same network; respondto the request by resolving the identifier of the target computingdevice into at least one of the internal address or the external addressof the target computing device and transmitting a result of resolvingthe identifier from the address resolution system to a source computingdevice associated with the request, wherein the address resolutionsystem resolves the identifier of the target computing device into theinternal address of the target computing device when it is determinedthat the source network and the target network are the same network, andwherein the address resolution system solves the identifier of thetarget computing device into the external address of the targetcomputing device when it is determined that the source network and thetarget network are not the same network.
 18. The non-transitory,computer-readable storage medium of claim 17, wherein the sourcecomputing device is configured to utilize the transmitted address tocommunicate with the target computing device.
 19. The non-transitory,computer-readable storage medium of claim 17, wherein the sourcecomputing device is hosted by at least one physical computing device.20. The non-transitory, computer-readable storage medium of claim 19,wherein the physical computing device is configured to transmit requestsfor resolution of addresses on behalf of the source computing devicefrom a source port of the physical computing device.
 21. Thenon-transitory, computer-readable storage medium of claim 19, whereinthe computer-executable instructions further cause the addressresolution system to determine a source network from which the requestwas received based at least in part on an address of the physicalcomputing device.
 22. The non-transitory, computer-readable storagemedium of claim 17, wherein the computer-executable instructions furthercause the address resolution system determine a source network fromwhich the request was received based at least in part on a source portof the request.
 23. The non-transitory, computer-readable storage mediumof claim 17, wherein the identifier of the target computing device is anetwork name of the target computing device.